In the manufacture of glazes for ceramics and porcelain enamel coatings for metals, it is often desired to form the raw materials into a frit; that is, a particulate glass-like product. The process involves blending the raw ingredients, melting the ingredients, quenching the melt and drying the quenched and shattered frit. While this patent application is not directly related to the mixing and melting processes, it should be understood that melting involves heating the ingredients until a fairly uniform molten glass is formed.
The principal object of quenching the molten glass as it emerges from the furnace in which it is melted is to make grinding of the solidified glass easier. If the glass is slowly cooled, it forms hard lumps which are difficult to crush or grind. Ideally, the quenched glass or frit comprises a particulate product having microcracks throughout each particle or chunk. It is desirable that the frit be as completely quenched as possible. Poorly quenched frits require much more time and energy to crush and grind (for example, in a ball mill) than well quenched frit. It is also important that the quenching be as uniform as possible. The uniformity of the frit can result in more uniform size of the crushed and milled frit.
Simply pouring the molten glass into a tank of quenching liquid, for example water, does not produce good quenching. The best quenching results from breaking up of the molten glass before or just after it enters the quenching water. Rapid cooling then causes shattering of the glass. A good frit is not only broken (shattered) into small pieces, but is intersected with cracks that makes further reduction in size easier.
A quenched and drained frit can comprise from 5 to 15 percent water. For transporting, batching, and milling, the frit preferably must be dried. Frit is usually shipped in paper bags and often in cardboard drums in which it must be dried.
If the frit is properly quenched using certain prior art methods, it does not contain sufficient heat to quickly self dry. The frit is not removed from the quenching bath until it has lost most of its heat. Then the frit is dried, for example, in a stationary or rotary dryer, which apparatus is energy inefficient. Dryers tend to generate much more heat than is actually needed to drive water off of the frit.
A process for quenching molten glass is described in U.S. Pat. Nos. 2,137,931 and 2,294,828. Drying of chopped glass strands with infrared heat is described in U.S. Pat. No. 4,024,647. Prolonging the cooling of frit by infrared heating on an oscillating conveyor is illustrated in U.S. Pat. No. 3,278,284. Drying porcelain enamel frit in a helical conveyor with hot air is illustrated in U.S. Pat. No. 2,688,807.
There has been a need for an extremely energy efficient system and method for quenching, drying and elevating frits. It is an advantage of this invention to provide such a system and method. The energy efficiency results from producing a well quenched frit that is drained of quenching liquid while it still retains sufficient heat to promote self drying with only the aid of infrared heating.